This invention is directed to a lens system particularly useful in motion picture filming of single strip 3-dimensional photographs.
Stereoscopic motion pictures require simultaneous exposure of left and right photographic images. These spaced images are later projected and keyed to each eye to provide binocular stereoscopy. An initial approach was to utilize two side-by-side movie cameras to expose separate films. This produced problems in maintaining synchronization, illumination and registration of the projected images, and the results impaired the 3-dimensional quality of the projected images. Thereupon, systems were developed that exposed the pair of left and right images on a single film strip. Side-by-side relationship of these images was not completely satisfactory and it has been considered preferable to expose the left and right images vertically with respect to each other on the film strip. Several complex optical systems have been developed in an attempt to satisfactorily accomplish the objective of satisfactory stereoscopic motion picture photography and projection. Such systems are found in R. V. Bernier U.S. Pat. No. 3,531,191, W. C. Hoch U.S. Pat. No. 3,825,328 and A. M. Marks, et al. U.S. Pat. No. 3,990,087.
These patents are burdened with complicated relay lens systems and complicated or special prisms for the folding optics. For example, the Bernier patent employs very complicated prisms and the configuration does not allow its use with modern reflex viewing motion picture cameras. In the Marks, et al. patent, the employment of a single final lens system to focus the image at the focal plane, using polarizing plates to minimize image bleed-over, causes the system to lose about 21/2 f stops of light with subsequent loss of desirable depth of field. The structure of the Hoch patent is similar in some respects and also has a complicated relay system. Therefore, there is need for a lens system particularly useful for motion picture filming for 3-D on a single film strip.